1. Field of the Invention
The present invention relates to an apparatus and method for evaluating subterranean environments to select a site for installation of a geologic depository facility of radioactive wastes and to evaluate the behaviors of waste materials and/or the performance of artificial barriers for geologic depository.
2. Description of the Related Art
Geologic depository has been studied as a method for treating high-level radioactive wastes (HLW) prepared by melting and solidifying glass materials in which waste liquids discarded from a nuclear reactor, etc. are sealed off, and various assessments have been made regarding safety of geologic depository. The term “geologic depository” means a disposal method of burying high-level radioactive wastes, of which decay heat has been suppressed to some extent, in a rock bed at a depth of 300 m or more, and storing them for a very long period in a condition isolated from zones of life.
Safety is the most important assessment item when selecting a site for construction of a geologic depository facility and specifications of the geologic depository facility. In other words, it is required to evaluate possibilities of migration of radionuclides by groundwater, etc. and migration to other types of nuclides, and to select the site and specifications so that radiation doses in the zones of life meet safety standards for a long future period.
The safety assessment is performed as follows. Various scenarios (such as a groundwater scenario and an approach scenario) are set for time-dependent changes of the high-level radioactive wastes buried deeply underground, and mathematical models for describing those scenarios are constructed. Various parameters (actually measured values and assumed values) affecting the migrations of nuclides are entered in the mathematical models to make computer simulation based on a great deal of computations, thereby determining the time-dependent changes of radiation doses in the zones of life.
There are various parameters for use in the safety assessment simulation. Examples of those parameters include ones characterizing chemical properties, such as the distribution coefficient (Kd) of a radionuclide in groundwater with respect to rock, the pH-value of the groundwater, the oxidation/reduction potentials of the groundwater, and the zeta potential of the groundwater, and others characterizing physical properties, such as the diffusion coefficient of rock, the water permeability coefficient of rock, and the temperature of the groundwater.
To measure those parameters, a rock sample and a groundwater sample must be obtained. According to a known method, for example, a pit is formed underground by boring. A rock sample and a groundwater sample are obtained from the pit and taken into a glove box installed in an experiment facility on the ground. Then, tests for measuring the parameters are performed in the glove box. A space in the glove box is adjusted to match with the atmospheric atmosphere in the underground pit from which the rock sample and the groundwater sample were obtained.